Cvetic, Gorazd

We use the known renormalon structure of Bjorken polarised sum rule (BSR) to evaluate the leading-twist part of that quantity. In addition, we include and Operator Product Expansion (OPE) terms and fit this expression to available experimental data for inelastic BSR. Since we use perturbative QCD (pQCD) coupling, which fails at low squared spacelike momenta due to Landau singularities, the fit is performed for where . Due to large BSR experimental uncertainties, the extracted value of the pQCD coupling has very large uncertainties, especially when is varied. However, when we fix the pQCD coupling to the known world average values, the and residue parameters can be determined within large but reasonable uncertainties.

Approximate knowledge of the renormalon structure of the Bjorken polarised sum rule (BSR) Γ\oline 1p‑n(Q2) leads to the corresponding BSR characteristic function that allows us to evaluate the leading-twist part of BSR. In our previous work [1], this evaluation (resummation) was performed using perturbative QCD (pQCD) coupling a(Q2)≡αs(Q2)/π in specific renormalisation schemes. In the present paper, we continue this work, by using instead holomorphic couplings [a(Q2)↦A(Q2)] that have no Landau singularities and thus require, in contrast to the pQCD case, no regularisation of the resummation formula. The D=2 and D=4 terms are included in the Operator Product Expansion (OPE) of inelastic BSR, and fits are performed to the available experimental data in a specific interval (Qmin2,Qmax2) where Qmax2=4.74GeV2. We needed relatively high Qmin2≈1.7GeV2 in the pQCD case since the pQCD coupling a(Q2) has Landau singularities at Q2≲1GeV2. Now, when holomorphic (AQCD) couplings A(Q2) are used, no such problems occur: for the 3δAQCD and 2δAQCD variants the preferred values are Qmin2≈0.6GeV2. The preferred values of αs in general cannot be unambiguously extracted, due to large uncertainties of the experimental BSR data. At a fixed value of αsMS\oline (MZ2), the values of the D=2 and D=4 residue parameters are determined in all cases, with the corresponding uncertainties.